This is designed specifically for the Primary Arms 1-6x LPVO scope. It fits snugly between the front objective and the factory lens cover. Simply remove the cover assemble, jam this in, and replace the lens cover. This is friction fit so if you are trying this on a similar sized scope and not the exact model, you may want to do a test print first since the taper geometry is fairly specific.  

What's this do? This prevents reflections from your scope from being seen. It will reduce the amount of light getting to your eye but its not much with 1-6x magnification so I'd suggest just running it in place always.  If you are trying to scale this up for a 18x+ scope you may have issues, but this works fine for what I designed it for. 

I included the STL as well as a 3mf for ABS. You can print this in anything, probably even TPU as long as you don't plan to leave the scope in the sun to get very hot.  To be safe, PETG is probably as low of a temp filament as I'd use.  These print settings can be easily adjusted. None of it is structural so 1 wall any material, whatever height you want. 

Print settings:
Layer Height: .28 mm (doesn't matter)

Walls: 1  (doesn't matter)

Infill: 5%